The South Africa exhibit at the San Diego Zoo Safari Park is home to more than 100 animals, and rhinos are at the top of the pecking order.

The sweeping enclosure is designed to replicate their African habitat. This is Jane Kennedy's domain. She is lead keeper and she knows many of the animals by name. The unquestioned star is Nola, a 40-something northern white rhino.

Kennedy's truck pulls up to Nola's feeding trough.

"So what we're doing here is preparing the medication for Nola," Kennedy said. "She's got a little bit of a sinus infection."

Kennedy delivers a plastic tub full of food pellets and apples with medicine sprinkled in.

Nola is a senior citizen nearing the end of her life, and Kennedy said that's why the sinus infection is so serious. The rhino gave keepers a scare in December when she first got sick. Nola's energy level plummeted as the sickness grabbed hold. But a few weeks of medicine and some hands-on care did a world of good.

Keepers are restoring her health, but the situation isn't so bright for her species.

War and poaching in the Democratic Republic of Congo extinguished northern white rhinos in the wild. Besides Nola, there is a northern white rhino in a Czech Republic zoo, and three more on a reserve in Kenya.

"I like to try to think that Nola isn't different than any other animal. But she is," Kennedy said. "She's one of five northern white rhinos left in the world. And what we humans do makes a difference for the extinction of this animal. I'm sorry, it makes a difference what we do here."

A large part of Kennedy's job with Nola is to make sure the animal is comfortable. It is hospice care. That can mean a friendly early-morning ear rub for the 4,000-pound animal. It can be making sure Nola gets the proper medical attention. Or it can be a comforting presence as she works through the final hours of life.

Kennedy is ready for whatever happens.

"I've known quite a few rhinos over the years. She truly is the sweetest rhino I've ever known. I can walk up to her any day and I can read her personality," Kennedy said. "And she sees me in the morning. She'll actually get up and she'll greet me. She'll make that shuffle and blow and it's like, 'Hi, Jane. How ya doing?' "

'Another Door Closing'

Nola's sudden December illness hit the Safari Park team especially hard because of Angalifu. The male northern white rhino died just a week before Nola got sick. He was old and suffering from arthritis, but the death was still unexpected.

"There's only one other male left. And unfortunately, he's not fertile. So this was the last fertile male that we had. And losing that, I mean, that was really tough because that was another door closing," said Randy Rieches, the San Diego Zoo Safari Park's curator of mammals.

That slamming door prompted a "Come to Jesus" meeting for zoo staff, Rieches said. Veterinarians, researchers, keepers and administrators did some soul-searching. They asked themselves if this was it. Was the northern white rhino essentially extinct? Did they fail?

"Every species that we have brought on grounds -- that we have put into our collection -- and we had a breeding group of, we have reproduced here. Except the northern white rhinoceros," Rieches said. "It's our only animal that we have not reproduced. And that in itself kinda goes down hard. But not to have reproduced it and then to watch it go down to extinction, that's something that none of us want to see."

Management, Conservation

But there is hope. There was a successful revitalization of the closely related southern white rhino. There were fewer than 100 of those animals a century ago. Careful management and conservation allowed the population to swell to more than 20,000 today.

At the San Diego Safari Park, more than 80 southern whites have been born. But that success story is the exception, not the rule for rhinos.

Southern white rhinos are the only rhino species not considered critically endangered. The large animals are poached and their habitat is squeezed.

Rieches worries the Javan rhino is slipping into the danger zone.

"With a species that has a 16-month gestation period and 3.5-year birth interval, they're only putting one calf on the ground every 3½  years. You have that in conjunction with the number that are being poached. We could be at the exact same place in a very short period of time with another of the rhino species," Rieches said.

Clock Keeps Ticking

Building the body of knowledge about rhinos is an ongoing process. Having success with one species could boost the future prospects of another. And the clock keeps ticking.

"Saving a species that still currently lives is one thing. Going back and looking at saving a species that has already passed into extinction is a whole other issue," Rieches said.

That puts the northern white rhino's future in the hands of researchers like Barbara Durrant. She filled a plastic tub with liquid nitrogen so she can show a box of frozen samples. The nitrogen is required to keep the samples colder than 135 degrees centigrade. Viability of the sperm degrades quickly at warmer temperatures.

These frozen samples could be a key to the northern white's future.

The sperm might be used to impregnate a southern white rhino female, creating a blended offspring, Durrant said. Tissue cells might be used to develop northern white eggs for laboratory fertilization. Or the frozen cells could be the basis for the development of a clone.

But there are limitations.

"We try to use the simplest possible technique that involves the least amount of manipulation. Because we change the way genes express themselves when we manipulate cells," Durrant said.

The science for reviving the northern white rhino in the lab is still being developed, but there is enough potential there to create hope. Durrant is confident that the species can still persevere, even if the five remaining rhinos die.

One Key Piece

"We can wait for the technology," Durrant said. "We can work on things in the meantime, with non-endangered model species. We can develop our skills. We can communicate with the other communities that are doing this work."

One key piece of the rhino's future lies in another tank full of frozen samples. It contains cell tissue from 12 individual northern white rhinos. That's a bigger pool of genetic diversity than what exists in the living population.

Durrant said researchers are working on techniques that will allow them to turn the tissue cells into eggs and sperm. She said that idea hasn't yet made the transition to the lab, but the potential energizes researchers.

"We're getting the foundation pieces together," Durrant said. "We're saving the things we need to save."

"Then we go one step at a time. I think what drives us is the image in our imagination of Angalifu's babies sometime in the future. A little rhino prancing in a field in South Africa that has Angi's genes," Durrant said.

The northern white rhino is likely rumbling toward extinction, but researchers hope that disappearance may not be permanent.

Update: San Diego Zoo Gets Funding To Help Save Northern White Rhinos